TBR Bio Sec II Q58

[milski]

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The passage talks about compliance (the ability of the arteries to expand when pressure increases) and has a graph how it decreases with age.

As compliance diminishes, it is most likely that peak arterial pressure occurs progressively:
A. earlier in systole
B. later in systole
C. earlier in diastole
D. later in diastole

My logic: obviously peak pressure will be during systole. If the compliance decreases and the artery is less "willing" to expand for the same squeezing force from the heart, it will reach maximum pressure earlier, since it needs less volume of blood for that to happen, thus A.

TBR's answer: B, since the passage mentions that "the heart is unable to eject its volume as rapidly as into a more compliant system" and if the heart ejects the volume slower, the max pressure will be reached later.

That does not make much sense to me. If there are no changes in the strength of the heart muscle (at least the passage does not mention anything like that), the only variable controlling how fast the blood is ejected is the pressure in the artery. If it raises quicker, the heart will be working against a higher pressure and will take more time to eject the volume for a single stroke but will still reach the max pressure earlier.

So... thoughts?

 

[sdm33]

You see the most important part is diastole, it is what determines systole pressure, and for most physiological changes it is the later diastole and later systole that determines what happens next.
so first we have the Venous return- then the End Diastloic ( EDV) - "preload"- then the Systolic (SV)-"Starling"
Ventricular P must exceed Aortic pressure during diastole for ejection, Ejection of end SV creates SBP in Aorta
DBP in the Aorta decreases delta P, and thus SV called "afterload"